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Cycles: bake transparent shadows for hair

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These transparent shadows can be expansive to evaluate. Especially on the
GPU they can lead to poor occupancy when only some pixels require many kernel
launches to trace and evaluate many layers of transparency.

Baked transparency allows tracing a single ray in many cases by accumulating
the throughput directly in the intersection program without recording hits
or evaluating shaders. Transparency is baked at curve vertices and
interpolated, for most shaders this will look practically the same as actual
shader evaluation.

Fixes T91428, performance regression with spring demo file due to transparent
hair, and makes it render significantly faster than Blender 2.93.

Differential Revision: https://developer.blender.org/D12880
This commit is contained in:
Brecht Van Lommel
2021-09-20 16:16:11 +02:00
parent d06828f0b8
commit fd77a28031
24 changed files with 500 additions and 110 deletions
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61
intern/cycles/render/geometry.cpp
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@@ -734,6 +734,10 @@ void GeometryManager::device_update_attributes(Device *device,
Shader *shader = static_cast<Shader *>(node);
geom_attributes[i].add(shader->attributes);
}
if (geom->is_hair() && static_cast<Hair *>(geom)->need_shadow_transparency()) {
geom_attributes[i].add(ATTR_STD_SHADOW_TRANSPARENCY);
}
}
/* convert object attributes to use the same data structures as geometry ones */
@@ -1659,6 +1663,7 @@ void GeometryManager::device_update(Device *device,
VLOG(1) << "Total " << scene->geometry.size() << " meshes.";
bool true_displacement_used = false;
bool curve_shadow_transparency_used = false;
size_t total_tess_needed = 0;
{
@@ -1669,26 +1674,33 @@ void GeometryManager::device_update(Device *device,
});
foreach (Geometry *geom, scene->geometry) {
if (geom->is_modified() &&
(geom->geometry_type == Geometry::MESH || geom->geometry_type == Geometry::VOLUME)) {
Mesh *mesh = static_cast<Mesh *>(geom);
if (geom->is_modified()) {
if ((geom->geometry_type == Geometry::MESH || geom->geometry_type == Geometry::VOLUME)) {
Mesh *mesh = static_cast<Mesh *>(geom);
/* Update normals. */
mesh->add_face_normals();
mesh->add_vertex_normals();
/* Update normals. */
mesh->add_face_normals();
mesh->add_vertex_normals();
if (mesh->need_attribute(scene, ATTR_STD_POSITION_UNDISPLACED)) {
mesh->add_undisplaced();
if (mesh->need_attribute(scene, ATTR_STD_POSITION_UNDISPLACED)) {
mesh->add_undisplaced();
}
/* Test if we need tessellation. */
if (mesh->need_tesselation()) {
total_tess_needed++;
}
/* Test if we need displacement. */
if (mesh->has_true_displacement()) {
true_displacement_used = true;
}
}
/* Test if we need tessellation. */
if (mesh->need_tesselation()) {
total_tess_needed++;
}
/* Test if we need displacement. */
if (mesh->has_true_displacement()) {
true_displacement_used = true;
else if (geom->geometry_type == Geometry::HAIR) {
Hair *hair = static_cast<Hair *>(geom);
if (hair->need_shadow_transparency()) {
curve_shadow_transparency_used = true;
}
}
if (progress.get_cancel()) {
@@ -1752,7 +1764,7 @@ void GeometryManager::device_update(Device *device,
/* Update images needed for true displacement. */
bool old_need_object_flags_update = false;
if (true_displacement_used) {
if (true_displacement_used || curve_shadow_transparency_used) {
scoped_callback_timer timer([scene](double time) {
if (scene->update_stats) {
scene->update_stats->geometry.times.add_entry(
@@ -1770,7 +1782,7 @@ void GeometryManager::device_update(Device *device,
const BVHLayout bvh_layout = BVHParams::best_bvh_layout(scene->params.bvh_layout,
device->get_bvh_layout_mask());
mesh_calc_offset(scene, bvh_layout);
if (true_displacement_used) {
if (true_displacement_used || curve_shadow_transparency_used) {
scoped_callback_timer timer([scene](double time) {
if (scene->update_stats) {
scene->update_stats->geometry.times.add_entry(
@@ -1795,8 +1807,9 @@ void GeometryManager::device_update(Device *device,
}
}
/* Update displacement. */
/* Update displacement and hair shadow transparency. */
bool displacement_done = false;
bool curve_shadow_transparency_done = false;
size_t num_bvh = 0;
{
@@ -1817,6 +1830,12 @@ void GeometryManager::device_update(Device *device,
displacement_done = true;
}
}
else if (geom->geometry_type == Geometry::HAIR) {
Hair *hair = static_cast<Hair *>(geom);
if (hair->update_shadow_transparency(device, scene, progress)) {
curve_shadow_transparency_done = true;
}
}
}
if (geom->is_modified() || geom->need_update_bvh_for_offset) {
@@ -1836,7 +1855,7 @@ void GeometryManager::device_update(Device *device,
}
/* Device re-update after displacement. */
if (displacement_done) {
if (displacement_done || curve_shadow_transparency_done) {
scoped_callback_timer timer([scene](double time) {
if (scene->update_stats) {
scene->update_stats->geometry.times.add_entry(